Dictys

Ok, on idle sat in heavy traffic with all lights on, a/c on, stereo on with car in "D" and foot brake the car develops a lumpy idle around 600- 650, with the dash lights dimming then brighting. If I put the car into "N" it will pick up to around 700 and the dash lights stop dimming then brighting.

The battery gauge normally shows 12v, but with the lights on and a/c etc drop towards 10v once I pick up speed it is back up to 12v. In the daytime I can also get the guage to drop if I put the a/c blower on max.

The CE panel has been refreshed and all the fuses and 53 relays have been replaced.

The battery was from PO and had discharged when I purchased the car, I charged it and it will still start the car without issue even if left for a week or more.

Is this a battery, alternator or something else issue? any ideas.

LGL

Go to your local Pep Boys and have a free alternator output check. It sounds like you don't have enough alternator output at idle speed to supply loads.

LGL

Forget the Pep Boys part. I just noticed your address.

Ethre

Alternator probably?

If it charges well when running above idle, then you're probably not getting enough output. Might be a good idea to check all the grounds (remembering the main engine ground) and clean them. Then check up the alternator.

WallyP

The alternator belt must be REALLY tight.

Use a voltmeter or multimeter to check the voltage at the jump start terminal. You should have 12.5 vdc or more with the engine off, 13.8 - 14.6 vdc with the engine running.

First thing to do is to clean ALL battery and ground connections. Needs doing even if it isn't the problem...

SteveG

+1 on the cleaning. The dimming sounds like alternator, probably should clean connections at alternator as well as 14 pin. From experience (currently, ha) I can say the batt can show 12.5 (off) and not have juice to start. You are flirting with a no-start.

M. Requin

+1 on grounds, esp the battery strap- inspect the area right where the insulation ends, often corroded. I'm betting on that and a bad battery.

Dictys

Tested the voltage at the jump point and it read 11.6 volts with the engine off ( couldn't start the engine as it was 5am and it would annoy next door), I have also cleaned most of the ground points (will do rest at weekend). So my plan is to buy a new battery as I think my alternator is putting all its effort into charging a dodgy battery, then if things haven't improved look at the alternator.

jon928se

PITA I know but check engine off voltage again at the battery and at the jump post.. If you're seeing 12.5 Vdc at the battery (as I suspect you will be) you have a high resistance somewhere between Battery -ve and earth and/or battery +ve to starter/alternator/jump point.

svp928

I had similar problem- lumpy idle,, rough running at low rpms...replaced the alternator with a Delco and was surprised at how big a difference it made in how the car ran. Much smoother with 14v showing from idle on up. Not necessarily a result of the Delco, just a good charging system at low rpms. If your alt is not working well, even a good battery won't keep the voltage up where the car likes it...
just my $.02...

Steve

928mac

Mine does the same and I have a 200 amp alt.
The problem is that when the idle is low that the alt can not charge.
You have to keep the engine/alt rpm at 600 or higher.
I put mine in neutral when I am slowing to a stop if I have a large draw (Head lights, heater blower stereo, Brake lights)
I am going to do a tune up this winter and then make sure that the idle is at 650 in gear.

dcrasta

600 is too low I believe the factory spec is 675+25 [Thanks Lizard931] rpms.

I would do this -

1-Ohm meter- inspect the Ground strap (remove from car/battery) Replace if resistance is detected (ohms) or if visually deteriorated.

2-CLean all battery terminals and connectors.

3-Clean all grounds

4-Clean the connector from the alternator to the harness. This is on the driver (left) side of the car near the powersteering reservoir (in a square plastic holder.)

5-Clean all connections near the 14 pin connect on the Passenger (Right) side near the jump post.

6-Inspect the alternator connector(s) on the rear of the alternator.

7-Inspect and adjust tension on the alternator ribbed belt.

8-Inspect and confirm condition of all vacuum lines

9-Adjust Idle speed according to FSM (make sure the idle speed adjustment is made correctly.)

10-Clean ICV (idle control valve) with some carb cleaner, follow with some wd-40 (lub) ..
------------

I did the first 8 steps and will be attempting #9 this weekend. made a big difference here .. Your mileage may vary. BTW most of these steps will cost you only your time and elbow grease..

Lizard928

actually the S4 is set to a very low idle.

Alan

If you really have <<~12.5v from the battery with engine off - you either have a bad battery (check battery terminal voltage) or a major connection problem from the starter/alternator to the jump post.

Then if you have checked battery & all these connections and you really still only have 12v at the jump post at high RPM you have a problem with the alternator.

Alan

dcrasta

Ahh, had to open the TechSpecs.PDF -

675+25 for the 87-89 . I believe he should set it on the high side (700) .

Thanks for pointing this out.